This invention relates to portable cellular radiotelephones adaptable for use in vehicular communications and, more particularly, to a power boost system for a portable radiotelephone wherein a power booster is automatically controlled by the radiotelephone.
Portable radiotelephones are readily carried about by a person so as to enable two-way conversation via a cellular telephone system from any of numerous locations, including a home, office, or outdoors. The radio telephone has a rechargeable battery to provide operating electric power, and transmits at a relatively low power level which is adequate in urban areas because transmission distances to a central cellular transmission/reception antenna are relatively short. At times, it may be desirable to operate the radiotelephone as a mobile telephone in a vehicle which is driven in rural areas, this necessitating transmission over a substantially larger distance from the radiotelephone to the base station antenna. In view of the increased distance, greater transmitted power from the radiotelephone is required, and a larger, more efficient antenna such as that carried by an automobile is preferred for both transmission and reception to insure high quality telephone communication.
One way of providing the higher transmitted power capability is to equip the radiotelephone with an outside higher-voltage source. However, this leads to increased weight, bulk and cost, and greatly diminishes the amplifier reliability of the radiotelephone. Also, excessive radiated power from a portable radio-telephone may present a health hazard. Thus, there is a need for providing a portable cellular radiotelephone with a means for adaptation to the mobile telephony situation wherein greater transmitted power is required, and wherein such adaptation can be accomplished automatically without assistance from the person using the telephone equipment. A problem exists in that presently available telephone equipment cannot fulfill this need in an economically feasible fashion with consideration to both architecture and implementation.